1994;153:3822C3830

1994;153:3822C3830. a trend toward protection against CD4+ T-lymphocyte loss was seen in these infected monkeys. These observations suggest that the V3 loop on some primary patient HIV-1 isolates may be a partially effective target for neutralizing antibodies induced by peptide immunogens. It has long been known that the strain-specific virus-neutralizing activity in the serum of human immunodeficiency virus type 1 (HIV-1)-infected individuals is mediated at least in part by antibodies that recognize a loop structure formed by a cysteine-cysteine bond in the third hypervariable domain of the surface gp120 (42, 45). This V3 loop is known as the principal neutralizing domain of T-cell-line-adapted (TCLA) strains of HIV-1 (15, 26, 31). The potential importance of the V3 loop as a target in the development of an HIV-1 vaccine was suggested by the finding that chimpanzees infused with a V3-specific neutralizing monoclonal antibody were passively protected from challenge with a TCLA strain of HIV-1 (10). Moreover, when chimpanzees were immunized with the envelope glycoprotein and then received a boosting immunization with the same V3 sequence peptide, they generated antibodies that neutralized HIV-1 in vitro and were protected from intravenous challenge with cell-free HIV-1 (12). The enthusiasm of investigators for pursuing Taranabant racemate a V3 loop-based strategy in HIV-1 vaccine development was, however, dampened by the observation that Taranabant racemate the V3 loop on the envelope glycoproteins of primary patient HIV-1 isolates can be relatively inaccessible to antibodies (1, 2, 36, 41). Nevertheless, interest in this antigenic domain of HIV-1 envelope as a target for antibody-mediated neutralization persists because of its importance in virus entry (6, 7, 21, 37C40, 43). One of the interesting and perhaps useful characteristics of the V3 loop with regard to a vaccine is that it can be mimicked by synthetic peptides. Not only do V3-specific antibodies in the serum of individuals infected with HIV-1 recognize synthetic peptides of the appropriate amino acid sequences (5, 34), but also HIV-1-neutralizing V3-specific antibodies Nr2f1 can be elicited by immunizing laboratory animals with synthetic peptides (14, 26, 27). Thus, a native three-dimensional antigen may not be required to elicit a V3 loop-specific antibody with anti-HIV-1 activity. In spite of the extensive work that has gone into characterizing the role of the V3 loop of the HIV-1 envelope in antibody-mediated viral neutralization, a V3 loop-based immunogen has not been carefully assessed for eliciting protection against a pathogenic viral challenge in a nonhuman primate species. In this regard, the recently developed simian-human immunodeficiency viruses (SHIVs) provide powerful tools for assessing the potential role of V3 loop-specific antibodies in vaccine-elicited protective immunity. SHIVs, viral constructs that express HIV-1 envelopes on a simian immunodeficiency virus (SIV) backbone, have been developed that Taranabant racemate express primary patient HIV-1 envelopes and induce AIDS in macaques. Such viral constructs can be used as challenge viruses in macaque species to evaluate the protection against infection conferred by vaccine-induced anti-HIV-1 Env antibodies (17, 30). The present study was done to determine the potential contribution of vaccine-elicited V3 loop-specific antibody protection against infection by SHIVs. Specifically, peptide-elicited anti-V3 loop antibody responses have been assessed for their ability to contain replication of SHIV-89.6, a nonpathogenic SHIV expressing a primary patient isolate HIV-1 envelope, as well as SHIV-89.6P, a pathogenic variant of that virus. MATERIALS AND METHODS Animals. Adult rhesus macaques were maintained in accordance with the guidelines of the Committee on Animals for the Harvard Medical School and the (Department of Health and Human Services publication 85-23, revised 1985). All monkeys were colony born and seronegative for simian retrovirus and simian T-lymphotropic virus type 1. Immunization. For each immunization, 1 mg of peptide was solubilized in 0.5 ml of phosphate-buffered saline and then emulsified with an equal volume of incomplete Freund’s adjuvant (Sigma, St. Louis, Mo.). The peptide emulsion (1 ml) was inoculated by the intramuscular route in four sites on the back of each animal. Virus stocks. Cell-free stocks of SHIV-89.6, SHIV-89.6P, SHIV-KB9, and SHIV-KU2 were produced in human peripheral blood mononuclear cells (PBMC) (23). Cell-free stocks of Taranabant racemate SHIV-HXBc2 and HIV-1 strains MN and SF2 were produced in H9 cells (25). Animal challenge stocks of SHIV-89.6 and SHIV-89.6P were prepared in rhesus macaque PBMC..